A differential interface is known as an interface which is hardly affected by noise. A differential signal line pair for transmitting a differential signal is used between semiconductor chips each having a differential interface. In design of a differential signal line pair in a circuit board (printed circuit board), various restrictions must be satisfied to obtain sufficient noise resistance.
PTL 1 describes a board, design program having an error check function of checking an error portion in which a differential impedance falls outside a reference range in the wiring pattern of a differential pair line (differential signal line pair).